The 100% focus loss is erroneously triggering when you finish the attack chain on Shellguard gauntlets.
This is because there must be an erroneous flag on the attack chain. The end of the chain ends in the front flip kick with the smash on the ground.
I bet that is getting flagged to be the same as the stamina rune attack. And stamina rune attacks are also bugged and triggering the 100% focus drain, even though they do not use focus.
Know what other rune is triggering the 100% focus lost on focus use pestilence affix? Channel utility rune, even though it does not use focus.
Video included in the drive folder.
This is horrible, I was lucky it was just Darak on pestilence lv4, because if it had been the Echo Knight or the Winged Brood or even River Twin, I would be forced to never have any focus to do a rune attack as the end of the attack chain drains all the focus.
Fixing the bug would be great, but deleting this horrid affix would be even better. This affix completely breaks builds as it makes channel skills unusable as they immediately drain all focus and stop channel skills immediately, and it discourages using low focus abilities as they drain the entire focus bar just like the 100-150 focus ones.